Ticketing is all handled offsite by EventBrite, so tickets and financial info are safe. They’ve redirected their URL to the Facebook page while they rebuild their website.
Lesson learned: Isolate your backups.
I don’t just mean physically. Yes, you need to keep some offsite in case the reason you lost your server is that the building caught fire. But isolate the online access as well. If you back up your site by pushing the backups from your server to a remote location (either self-hosted or cloud storage like Dropbox or Amazon S3), those credentials are stored on your server somehow. What could an attacker do with them?
Consider: If someone breaks into your web server, what else can they do in addition to vandalizing your site? Can they access other databases? Can they hop onto your internal network? Retrieve or alter private files? Can they get at your backups? If so, can they get at all your backups including private documents?
The answers are going to depend on your network and backup setup. But they’re questions you need to start asking.